How Effective is the Flu Vaccine? Surprising New Data…

It’s that time of year again: flu shots are here. We all are a bit shell-shocked after last year’s H1N1 pandemic madness, and many communites were divided on the pros and cons of the flu vaccine. So who really needs the annual flu shot? There’s actually a very comprehensive new study which should help shed some light on this issue.

First, let’s just review the flu vaccine; available each fall, it’s a worldwide standardized collection of 3 influenza viruses that are presumed to be the upcoming season’s likely virus. This 2010 vaccine, just now available, also includes the H1N1 strain as one of the three strains. As I mentioned a couple weeks ago, the H1N1 pandemic was officially declared over but it is still around and may still flare up. More importantly, it never became the deadly pandemic we had feared it might. However, parents should know that H1N1 was more selectively deadly to toddlers and pregnant women, with the death rate for children over four times higher than is usual for the flu season, as you see in this graph from the American Academy of Pediatrics 2010 Policy Statement on Influenza:

The AAP recommends annual trivalent seasonal influenza immunization for all children and adolescents 6 months of age and older. Special efforts should be made to immunize all family members, household contacts, and out-of-home care providers of children who are younger than 5 years; children with high-risk conditions (e.g., asthma, diabetes, or neurologic disorders); health care personnel; and pregnant women. These groups are most vulnerable to influenza-related complications.

Over 200 viruses cause influenza and influenza-like illness which produce the same symptoms (fever, headache, aches and pains, cough and runny noses). Without laboratory tests, doctors cannot tell the two illnesses apart. Both last for days and rarely lead to death or serious illness. At best, vaccines might be effective against only influenza A and B, which represent about 10% of all circulating viruses. Each year, the World Health Organization recommends which viral strains should be included in vaccinations for the forthcoming season.

Authors of this review assessed all trials that compared vaccinated people with unvaccinated people. The combined results of these trials showed that under ideal conditions (vaccine completely matching circulating viral configuration) 33 healthy adults need to be vaccinated to avoid one set of influenza symptoms. In average conditions (partially matching vaccine) 100 people need to be vaccinated to avoid one set of influenza symptoms. Vaccine use did not affect the number of people hospitalised or working days lost but caused one case of Guillian-Barré syndrome (a major neurological condition leading to paralysis) for every one million vaccinations. Fifteen of the 36 trials were funded by vaccine companies and four had no funding declaration. Our results may be an optimistic estimate because company-sponsored influenza vaccines trials tend to produce results favorable to their products and some of the evidence comes from trials carried out in ideal viral circulation and matching conditions and because the harms evidence base is limited.

It is indeed disturbing that the Cochrane group found that “there is evidence of widespread manipulation of conclusions and spurious notoriety of the studies“, that “reliable evidence on influenza vaccines is thin“, and that “our results may be an optimistic estimate.”

Please note that this study only covered healthy adults and not children. The Cochrane group in 2007 reviewed the flu vaccines for children and found fair effectiveness in children over, but not under, 2 years:

The review authors found that in children aged from two years, nasal spray vaccines made from weakened influenza viruses were better at preventing illness caused by the influenza virus (82% of illnesses were prevented) than injected vaccines made from the killed virus (59%). Neither type was particularly good at preventing ‘flu-like illness’ caused by other types of viruses (33% and 36% respectively). In children under the age of two, the efficacy of inactivated vaccine was similar to placebo. It was not possible to analyse the safety of vaccines from the studies due to the lack of standardisation in the information given but very little information was found on the safety of inactivated vaccines, the most commonly used vaccine, in young children.

My Bottom Line

I do find the latest Cochrane meta-analyses very disturbing, and I am not as gung-ho as I was in previous years. However, I still recommend the flu vaccine for all my patients, and certainly for myself, my co-workers and my family. Perhaps it’s not as effective as we thought, but it still offers at least partial protection, and I am comfortable with the risk/benefit balance. But families and readers need to make up their own minds.

I still mostly recommend the vaccine especially for anyone in contact with infants, especially under 6 months, as well as frail elderly people. Those groups, especially the infants, are most vulnerable to any complications of the flu, and many die each year from complications. And since infants under 6 months aren’t eligible for the vaccine, their best protection is prevention of exposure — to have their loved ones and caretakers be as immune to the flu as possible. So while the vaccine may offer only partial protection, it’s still the best we have.